Pulmonary surfactant is believed to be synthesized and largely stored by the fetal lung and not released into the alveoli in any appreciable amount until after birth and breathing. Although the biochemistry of lung maturation and surfactant production and its acceleration by hormones has been studied extensively in the fetal animal, very little is known about the factors which control surfactant production (release and/or synthesis) at the time of birth and in the immediate postnatal period. We propose to study the influence of a number of factors, including normal and induced labor, gestational age at delivery and breathing, on surfactant secretion and synthesis in the newborn rabbit. The parameters of production will include phospholipid content and composition of lung lavage, activities of several enzymes of pulmonary phospholipid biosynthesis and net synthesis of phosphatidylcholine in lung slices. In addition, using this model we will study the effects of a number of hormones and other pharmacological agents on surfactant production in the postnatal period. These will include corticosteroids, thyroxine, metyrapone (an inhibitor of endogenous cortical synthesis), colchicine, sympathomimetic agents and their antagonists and agents which increase endogenous levels of cAMP. These studies will, therefore, yield basic information on the mechanism of surfactant production and indicate which agents and factors are physiologically involved in this process. In addition they may indicate agents which might potentially be used in the stimulation of surfactant production. This is of clinical relevance since insufficient surfactant is believed to be the cause of the Respiratory Distress Syndrome of the newborn - the major cause of morbidity and mortality among premature infants in the United States.